That's a great idea. Another way of doing this is to use Google map. Google map already knows your location for their collection of traffic data [1], they could

That's a great idea. Another way of doing this is to use Google map. Google map already knows your location for their collection of traffic data [1], they could cross reference this to when they car leaves a parking location. The emptying of the car park is notified to Google map. Trouble is the data is only available to Google. [1] http://www.theconnectivist.com/2013/07/how-google-tracks-traffic/ http://www.theconnectivist.com/2013/07/how-google-tracks-tra...